This invention relates to an improvement in a system for casting concrete panels and particularly to a single pass casting operation wherein slip forms are utilized to form core areas and deliver panel core material into these areas. The core material is dumped from the cores after at least partial curing of the panel.
A machine for forming such hollow core panels in a single casting operation is disclosed in U.S. Pat. No. 4,369,153. In that machine (and in earlier machines requiring two casting passes to form hollow core concrete planks such as are shown in U.S. Pat. No. 3,217,375 and U.S. Pat. No. 3,523,343), the concrete plank is formed on an extremely long casting bed which generally has a length in the 500' to 680' range. Prestressing cables are attached to stressing abutments at opposites ends of the bed. The cables are put under high tension prior to the commencement of casting. Despite the tensioning of the cables, they have a tendency to droop and/or move transversely from the desired position during casting of the concrete. Typically the casting machine has a strand guide suspended from it which guides the reinforcing strand as the concrete is being cast around it so that the strand is directed into approximately the correct position in the web between adjacent hollow cores.
Although plastic clips or chairs have been used to support rebar (reinforcing, unstressed steel) in various concrete applications, those clips generally have only a single cable supporting cup and are ordinarily suitable for supporting rebar between 1/2" and 3/4" above the surface of the casting pallet. Such prior art clips and chairs are not suitable for supporting top strand as a hollow core concrete slab is cast on a single pass casting machine such as the one in U.S. Pat. No. 4,369,153.